106 NEW YORK STATE MUSEUM 



beds, but have not been observed farther west. They are evi- 

 dently survivors clinging to the eastern region. The pygidia of 

 Cybele observed at Rysedorph hill and stage N of the Que- 

 bec group in Newfoundland belong to forms closely related, if 

 not identical with the European y b e 1 e verrucosa. 



There are still other differences in these faunas mani- 

 fested in the distribution of forms known before. Thus 

 the genus Triplecia, occurring in the lower Trenton pebbles of 

 Rysedorph hill, is represented in the Trenton of New York by 

 three species, while, according to Schuchert's Synopsis of 

 American fossil Brachiopoda and Winchell and Ulrich's lists, 

 it is not found in Trenton beds west of New York, but appears 

 in the central region in Lorraine time and continues into the 

 Niagara period. In Europe several species from the lower 

 Siluric have been referred to this genus, one of which, 

 Triplecia spiriferoides McCoy, from the homotaxial 

 Llandeilo, belongs to the radiated group represented in the 

 eastern Beekmantown limestone. O r t k i s i n s u 1 a r i s Eich- 

 wald is also regarded as a Triplecia by Hall and Clarke. This 

 ranges from the Llandeilo to the upper Llandovery. It is there- 

 fore probable that the peculiar distribution of this genus in the 

 Trenton of America indicates zoogeographic differences between 

 the eastern border and the more continental Trenton, due to the 

 exchange with the faunas of more easterly regions. 



Tri nucleus concentricus has been recorded from the 

 lower Trenton of New York (White, p. 84) and abounds in the 

 upper strata of this formation, but it does not appear as a Tren- 

 ton species in the lists of Minnesota fossils given by Winchell, 

 Ulrich and Clarke. In the Ohio valley it pertains to the upper 

 beds only (i. e. upper Trenton and Richmond). This species 

 seems to have slowly spread from east to west into the continen- 

 tal basin, No other species of this genus is known in the North 

 American lower Siluric, with the exception of a small Utica 

 form, separated by Ulrich, while in Europe quite a number of 

 lower Siluric species have been described. These facts appear 



